The present invention relates to a communications device that functions as a light transponder that is simple and robust and is suitable for use as a personal information carrier such as an identity card.
Identity cards and other information carriers such as bar codes applied to labels on retail products are commonly use in todays world to enable the people and products assigned with such cards and bar codes to be recognised in an increasingly mechanised and computer controlled environment. To date the development of such information carriers has focused on increasing the amount of fixed information that can be displayed and on the creation of xe2x80x98smart cardsxe2x80x99 which are interactive in a computerised environment. In the case of a personal information carrier, for example a travel permit, information is recorded on a magnetic strip that must be passed through a reader to enable the information stored on the card to be read. Similarly, bar codes applied to labels on products are read by a hand-held reader or by a static reader across which the bar code is swiped.
In U.S. Pat. No. 4,983,021 a reflector system is described that is particularly suited for use in the location of an object at a distance. A retroreflecting surface is used to reflect electromagnetic radiation back to a receiver adjacent a transmitter of electromagnetic radiation along the incident path. A separate shutter is provided in front of the retroreflector to selectively interrupt the path of the reflected light and thereby modulate the reflected light. For example, where the shutter is a liquid crystal, the transparency of the liquid crystal is altered from a transparent state to an opaque state.
The present invention seeks to provide a communications device that is suitable for use as a personal information carrier which is simple in construction and for which manufacturing costs are low. Moreover, as a personal information carrier the present invention seeks to provide an optical means (i.e. non-contacting) that is capable of supplying information stored in the device without the need for the carrier to be swiped across a reader. The invention further seeks to provide a communications device that requires only a very small, if any, power supply such as that provided by solar cells.
The present invention provides a communications device comprising a radiation sensor, an adjustable reflection layer having a surface contoured with a retroreflecting shape, modulating means for altering the reflection characteristics of the adjustable reflection layer and a controller in communication with the sensor and the modulating means for controlling changes in the reflection characteristics.
Preferably, the adjustable reflection layer consists of a material having an electric field dependent refractive index in which case the modulation means may comprise biasing means for applying an electric field across the adjustable reflection layer.
In a preferred embodiment the contoured surface of the adjustable reflection layer is in contact with an outer layer that is substantially transparent to incident radiation whereby the refractive index of the adjustable reflection layer is adjustable between a refractive index substantially the same as the refractive index of the outer layer and a refractive index different to the refractive index of the outer layer. A further outer layer may be provided in contact with a surface of the adjustable reflection layer opposite the contoured surface, the interface of the further outer surface and the adjustable reflection layer forming a scattering interface in front of the contoured surface whereby the modulating means adjusts the degree of radiation scattering caused by the scattering interface.
In an alternative embodiment the modulation means comprises a piezoelectric layer in contact with the adjustable reflection layer for applying mechanical vibration to the adjustable reflection layer.
The retroreflected radiation may be amplitude modulated by the adjustable reflection layer. Alternatively or in addition, the retroreflected radiation may be phase/polarisation modulated by the adjustable reflection layer.
It will be understood that reference herein to a surface contoured with a retroreflecting shape is intended as reference to a surface having a repeating three dimensional pattern that is retroreflecting.